Foamie aerodynamics.

[WesGrimes]

The more inportant part of the illustration is the size of the gap between the cab and trailer and how the curved roof of the trailer follows the line of the cab deflector. Not easity reproduced with a car and a bumper pulled trailer.

I wander if some flexible fairing would work to fill the gap?

http://www.freightwing.com/gap_fairing.php

[Bogo]

Not exactly the same, but seams relevent:

I've been thinking about aerodynamics allot and looking at what others have done in the past. Take a look at the turbulence bubble over the top front of the flat topped trailer. It extends up about as much as the curved trailer top does. Likely there isn't much effective difference in frontal area. The dropped back shippers will hate as it reduces access. That trailer would have to be side loaded which most loading docks aren't setup for. One thing to remember is most wind tunnel stuff like this is done with the wind being perfectly aligned to the vehicle. That is rarely the case. More often than not there is some side wind component that shifts the direction some to the side. That really changes the airflow between the tow vehicle and trailer.

This shape brings up lots of what I've been thinking about these past couple weeks. I've been toying with making a hard sided pop-up. The top will be highly streamlined, with a straight walled bottom. While I can't make the gap between the tow vehicle and trailer smaller using a bumper hitch, I can better deal with the air coming off the vehicle and hitting the trailer. So far I'm looking at a smooth rounded bubble leading smoothly into a very gently arched roof. The front bubble will have storage in it that is accessible from the inside when the top is up. The arching of the top in the middle allows for greater headroom than would be possible with the height of lift. The back will be sloped down like the Prius is, and will extend back further than the interior. This will allow the tail to be drop further for a smaller rear vacuum zone. The extension will also allow for more storage.

I want a hard sided pop-up because of bear territory, the desire for a built in shower, toilet, and kitchen as well as having a double sized bed. I want to cram that all into the smallest volume that is realistic, and still allow the bed and toilet to be used at the same time. I'm also toying with having the lift in the front be more than the rear. That has it's own fitment issues, but that can be dealt with. It will allow for an even lower rear end as well as still provide the needed headroom over the kitchen/bathroom area. A basement is also being looked at. It increases overall height, but the travel height is only raised by half the basement height. On the other hand it allows for a smooth underbelly. Especially if the main frame the axle is attached to is just below floor level, and the basement is suspended under it. Wheels will be in fender wells that will be covered over by the top when lowered. Actually I will likely have a plate of metal on the outside of the wheel well that will keep splash from hitting the inside of the top. That plate of metal will be removable for tire changing. It will also help contain a shredded tire so the top isn't damaged.

It's an interesting puzzle to fit it all in, and have the design look nice when done.

[atahoekid]

Sounds interesting. Would love to see concept sketches.

[GPW]

Aerodynamics is one reason we went with the FoamStream idea ... All rounded surfaces ... Sharp edges cause vortices to form , and that’s drag too ...
Problem with drag reduction is once you take care of the major Drag producers , it takes increasingly more elaborate measures to save Smaller amounts of Drag .. with diminishing returns for the effort involved... There are limitations to the amount Drag can be practically reduced... so we’re stuck with some drag ...despite our efforts ...
The theoretical idea for a trailer would look like the Goodyear Blimp ... with faired in wheels and recessed fixtures (vents , door handles, etc. ) Still it does have to displace “X” amount of air , so there will always be some Drag ...
With our trailers we must expect (accept) a practical Compromise between comfort , build-ability, and skills involved vs aerodynamics ....

Probably our main motivation to reduce Drag is the price of Gas ... Easiest way to reduce Drag and save Gas is to SLOW DOWN .... Drag increases with Speed .... a LOT !!!! If you’re going camping or just traveling , you may want to slow down and just enjoy the ride ....
Although driving around a city is not enjoyable for me , there’s nothing like a nice ride across the country to see new things and take in the sights .... More difficult at 85mph... more costly ...

[Wobbly Wheels]

Just sort a random thought here after looking at the wind tunnel pics - I'm not really sure how it would apply to trailer building...
I think it's pretty intuitive that the red areas would need to be 'filled in' or skinned over (where practical) to give the airflow something to stick to (laminar flow), but of course that creates a somewhat impractical shape.

Perhaps one could reduce that compromise by having a top made of fabric rather than a solid structure ?
I'm not talking about fixing the cloth rigid with bows but allowing it to float in the airflow. More like how one 'flies' a sail than a convertible top. When sailing, one trims the sail to balance the high and low pressure sides of the sail so that the sail rides in between them as much as possible. You are watching the luff (back edge of the sail) for fluttering, meaning that you're out of the 'sweet spot'.
What if we could make a fabric top that would be light enough for the low pressure (red areas) to 'suck' the cloth up where necessary so that it forms its own shape and automatically adjusts for road speed ?
Something like 1/2oz spinnaker cloth (nylon) might be light enough to do the job and still keep the rain off you as you slept. Military surplus parachutes are lightweight and cheap.

Dunno, just kicking around an idea that might have no practical application - I wonder if the fuel economy would be improved enough to justify the effort.

[Bogo]

Sounds interesting. Would love to see concept sketches.

I've been working on them. I figured out why Sketchup wasn't working and have been playing. For the rear, think Prius back half, but boxier sides due to needing to fit over the bottom. The front will likely continue the curve of the top to a well rounded front. I'm figuring on combination of carved block and strip plank foam construction at this point so it shouldn't be too complex to make. The middle sides will be boxy due to needing to fit over the bottom half. I may pinch in the sides at the rear, but it won't be by much. Maybe a couple inches. I'll mainly be putting the streamlining into the top profile and front. I expect the overhang beyond the bottom will only be two feet or so.

Considering I'm already a slow poke on vacation. Slowing down isn't going to get me that much gain. Where I'll need the streamlining is when I'm on business.

[GPW]

This may be an odd thought ... I have an extremely long tongue on my FS designated trailer, the plan was to cut it shorter , but the thought occurred by making the trailer further back , might put it in “cleaner” air , lessening the interaction between it and the Tow vehicle ... crumbs for thought... ???

[Bogo]

My thought on tongue length is the shorter the better. Most often you have some side wind and not a pure head wind. With a shorter length less air gets inbetween. Any air that isn't in the tail wake of the tow vehicle needs to be pushed out of the way by the front of the trailer which means more effective frontal area. With a longer tongue there is more distance for the wake to diminish in size so more air is needed to be pushed out of the way. The before streamlining semi trailer image shows that wake and how it trails off in size as the distance behind the trailer gets further and further. Now, the aerodynamics between tow vehicle and trailer are a bit different than the tail wake image implies. A very turbulent region of air ends up somewhat pulled along by the tow vehicle as well as somewhat pushed along by the trailer. The thing is side winds push some of that air out to the down wind side and part of the upwind side of the trailer gets to fully part the air stream. The further the trailer is back, the more the side wind can push air out from between the vehicles and thus more air is needing to be parted by the front of the trailer. Some side wind is the norm.

Not described as well as I'd like, but I have fields to harvest.

[GPW]

Yes, I can see it now ! Thanks for that !!!

[linuxmanxxx]

Look at nascar unless 2 cars tag up at the front and rear bumpers and "push" in tandem, they are slower and have lots of dirty air drag on the car surfaces. At high speed and such sleek low lines imagine what a larger gap and larger items do in dirty air. This lends to yes shorter tongue and either same or smaller profile are your best options for reduced drag.

[ghcoe]

That is why they follow so close in nascar too. They are drafting behind the the car in front of them.
My friend told me that when he was younger, and braver, he would get behind a semi and draft behind them. He said there was so much of a suction that sometimes he would have to hit the brakes to avoid hitting the back of the truck.

[GPW]

Logically , all this aerodynamics concludes with a one piece vehicle... No tow , less Drag ... If you tow anything , you’re gonna’ get “some” drag ... Plus the weight factor ... Lighter saves gas too ...

[angib]

I have often wondered if you can reduce drag by trying to make the trailer ride height as close to possible as the tow vehicle.

I don't think a trailer bottom that's higher than the two vehicle's is any problem - that is all disturbed air, not smooth flow, coming under the two vehicle. But I do think a trailer bottom that's lower than the two vehicle is a bad idea as then the surplus air has to be shunted round the sides.

....by making the trailer further back , might put it in “cleaner” air , lessening the interaction between it and the Tow vehicle

Yes, but you don't want that result. Putting the trailer further back will increase drag since the trailer won't be in the tow vehicle's wake.

Note that teardrops and travel trailers are not the same in this respect as the travel trailer is typically bigger than the tow vehicle, so it's 'out in the breeze' whatever the gap is. Whereas a teardrop is typically a similar size to the tow vehicle, so it can ride inside its wake, if close enough.

[Bogo]

Note that teardrops and travel trailers are not the same in this respect as the travel trailer is typically bigger than the tow vehicle, so it's 'out in the breeze' whatever the gap is. Whereas a teardrop is typically a similar size to the tow vehicle, so it can ride inside its wake, if close enough.

From that wind tunnel image of the truck, notice how fast the wake decreases in size. When the tow vehicle is well streamlined, it reduces in size much faster. I'm not sure there is much you can do other than make the front of the trailer streamlined so it parts the tow vehicle's wake as smoothly as possible. Sure there will be a zone where the tow vehicle's wake joins up with the air pushed forward by the trailer, but that will only be some fraction of the height of the rear of the tow vehicle. With a car like the Prius, I'd bet it ends up being less than 50%.

[Bogo]

Without NURBS to play with, this is what you get for a rough sketch. I quick threw in a model for scale, and some colors. I also haven't sketched in details like the fender wells, door, windows, etc.. For scale, the model is 5' 9" tall with heals and hat. The marble surface is the counter top. On the bed end I'll leave space for a coffee maker. Got to have easy access to it in the morning. Under it will be the refrigerator. Next on the counter top will be a two burner ceramic electric cooktop. Then a sink, and finally a bit more counter space. The floor in front of the kitchen counter is dropped because it is the shower drain pan. At the front end of it will be where the toilet goes. The bed is a standard double sized bed. It will fold against the wall into a couch, and a couple table sections can be mounted to the opposite wall. Tire size is the same as my 4Runner uses. I can get hubs that have the same bolt circle that Toyota uses on the 4Runner.

Top down



Top removed to see interior.


Cut away to better see floor details.


The overall height of the trailer is roughly 5' 6", but I think I can reduce that at least 4". Ground clearance is 12". It should handle some off road use. As drawn the bottom box is 12' long, and 5' wide.(fixed width) I think I can reduce up to 18" from that length. The top is 16' long from curve front to the rear wall. The top lifts with roughly 3' 6" lift at the front and 2' 6" lift at the rear. All numbers are in flux as this is just initial drawings to get an idea how things will work. I already see the wheel well will intrude into the area I was thinking of using to stow the TV/computer monitor. The counter is 5' 8" long, 24" deep. The shower drain pan floor is 5' 8" long and 2' 8" wide, and recessed 3" lower than the normal floor level. I'm a little worried the shower floor would be a bit narrow. I may be able to make the counter a bit less deep, or widen the bottom by an inch or two. Much more than that and I'm getting wider than the 4Runner.

I figured out how to make overhead cabinets for the kitchen. Use KV 82 decorative heavy duty shelf standards and brackets. On the lifting top's wall behind the cabinet, mount the standards. They will need to be recessed into the wall some. The shelf brackets then can be used to support boxes that provide the overhead cabinets. I could even hold up a convection toaster oven this way. For travel the cabinets would be placed on the floor and strapped down so they don't move. The table across from the couch could also be held up with shelf brackets. BTW, a pair should hold 350 to 400 pounds if the standard is mounted properly. The brackets are available in lengths up to 24".

I also got the crazy idea of making a portion of the roof top surface clear lexan and putting a few solar panels under it, and above the insulation. That would allow solar without hurting airflow.

I decided on electric cooking because I can always use a camp stove outside, and this way the exhaust fan won't have to work to remove propane combustion gasses. I was thinking of putting a platform for a 3kW Honda inverter generator on the tongue. That would require modifying the top design to cover it over while driving.

Propane tanks for heating. My current thought for placement is making a spot for two 40 pound horizontal mount portable tanks under the couch base. The other option is making an outside vented compartment for the generator there, and putting a pair of 40 pound vertical tanks on the tongue.

(Edit: I fixed the width of the lower box from 6' to 5' wide. I should be more careful when posting during the middle of the night.)